Time delay relay



June 24, 1947. Rm 2,422,986

' 'mna nsmx RELAY Filed lay 10, 1944 Invntor: Robert. C. 'R'ng,

Patented June 24, 1947 'rmn DELAY nnunz--- Robert 0. Ring, Schenectady, N. Y., asslgnor to General Electric Company, a corporation of New York Application May 10, 1944, sci-in No. 534,980

Claims. (Cl. 175-372) My invention relates to time element electromagnets, and particularly to time delay electromagnets of the type having a non-magnetic, low resistance electric conducting material encircling the core to delay the decay of flux in the core.

Electromagnetic time delay relays are commonly provided with short-circuited copper rings surrounding a portion of the-magnetic circuit for the purpose of restraining the decay of flux in the magnetic circuit when the exciting coil is deenergized. In some such relays, the shortcircuited turn takes the form of a sleeve of copper or some other non-magnetic, low resistance electric conducting material encircling a straight portion of the core within the coil spool. In the typical electromagnetic time delay relay, however, the complete core includes, in addition to the portion within the coil, a return magnetic path either through'air or through one or more separate magnetizable core members, bolted or otherwise secured to the coil core. In multi-section core structures of this type the copper-encased coil core is but a small part of the entire core structure. Furthermore, the core reluctance is quite large because small air gaps unavoidably exist between the connected sections of the core.

In certain applications where weight and volume are of importance, it is essential t avoid all unnecessary air gaps in the magnetic circuit so that the cross section of iron and the size of the exciting coil may be held to a minimum. At the same time, it is desirable, in order to obtain the greatest possible time delay in a relay of predetermined size and weight, that the copper sleeve encircle as much as possible of the magnetic circuit.

According to my invention, I provide a time delay electromagnetic relay which is small in size, rugged, light, simple to manufacture, eflicient in operation, and characterized by a minimum number of air gaps in the magnetic circuit. This I accomplish by encasing an integral core member of solid magnetizable material for substantially its entire length in a sleeve of copper or other non-magnetic low resistance electric conducting material, and bending the core member and sleeve together to bring the ends of the core closely adjacent to each other. In this way, the encased core member forms a large part of the complete magnetic circuit, since only a short armature need be interposed between the juxtaposed pole faces to complete the magnetic circuit. Furthermore, since the decay of flux is retarded to the utmost by the great length of copper sleeve, the necessary initial value of flux is reduced, thereby minimizing the necessary cross section of iron. The necessary cross section of iron is further held to a minimum by the fact that the unitary core structure provided avoids all unnecmsary air gaps.- Furthermore, the one piece structure is sturdy, inexpensive, and quickly and easily manufactured.

For a more complete understanding of my invention, reference may now be had to the following detailed description taken in conjunction with the accompanying drawing in which Figs. 1, 2, and 3 are front, side,'and bottom views, respectively, of an electromagnetic time delay relay embodying my invention; and Fig. 4 is acrosssectional view of. the relay core taken along the line 4-4 of Fig. 1.

Referring now more particularly to the drawing, the relay therein illustrated upon a base I which may suitably be formed of a molded plastic insulating material of any desired well-known type. The relay frame comprises av Ueshaped magnetizable core member 2 encased for substantially its entire length in a sleeve 3 of copper or other non-magnetic low resistance electric conducting material, and a magnetizable pole piece 211 which is attached to one polar end of the core member 2 by a bolt 4. The relay includes also a movable armature i positioned in attractive relation with respect to the pole piece 2a and the pole face at the opposite polar end of the U-shaped core member 2. The armature 5 is oflset at its center so that it cooperates with the upper surface of the pole piece 2a and the downwardly directed pole face at the opposite,

end of U-shaped core member 2. The armature is rotatably mounted at its center upon a bolt 8 which passes through a pair of spaced upturned bearing arms 1 forming part of a non magnetic supporting bracket 8 of brass or other suitable material. The supporting bracket 8 is attached at one end to the pole piece 2a by the bolt 4 and at its other end to the opposite end of the magnetic core member2 by a bolt 8. By means of the bolt 9 there is also attached to the core 2 a flat strip ill of insulating material upon which is mounted a pair of stationary contacts i I electrically connected to suitable terminal connectors I2. To the armature 5 there is attached a pair of movable contacts l3 for cooperation with the fixed contacts II.

The armature 5 is biased to a normal position spaced from the oppositely disposed pole faces at the ends of the U-shaped frame 2, 2a by means of a compression spring ll interposed between one end of the armature and an adjustable bolt l5 threaded into an oflset portion ii of the supporting bracket 8. The adjusting bolt i5 is provided with an annular spring seat H. The air gap between the core and armature may be adjusted by means of an armature stop bolt l8 adJustably mounted in the supporting bracket 8.

For the purpose of establishing a magnetic flux through the frame and armature I, an exciting winding may be mounted to encircle any desired portion of the U-shaped core member 2. In the drawing, I have shown my relay provided with a pair of pre-formed exciting coils l 9 and 20, wound upon spools and mounted adjacent each other on the parallelly disposed legs of the U-shaped core member.' The two windings i9 and 20 may be arranged to establish fluxes either in like or opposite directions. If the coils are arranged in aiding relation, their effect is simila in principle to that of a single winding, but by distribution of the winding into two coils there is less leakage flux present. If, on the other hand, the coils are arranged to establish fluxes in opposing relation, the relay may be energized by either coil alone and deenergized either by deenergization of the exciting coil or by equal and opposite energization of the other or neutralizing coil. The lead-in wires to the coils I9 and 20 are brought out through suitable terminal connectors, such as 2| and 22.

It is sometimes found desirable to introduce into the magnetic circuit a fixed controllable air gap in order to reduce the residual flux in the magnetic circuit and thereby to permit armature drop-out at a low flux value. Such a gap may be introduced by a shim 23 between the pole piece 2a and the adjacent end of the U-shaped core member 2. Th shim 23 may suitably be made of brass Or other non-magnetic material, or, if only a very thin shim is desired, its mechanical strength may be increased by plating the brass upon a small wafer of steel. The shim has very little effect upon the maximum flux.

While it will be understood that the magnetizable core member 2 may be of any desired crosssectional configuration, so long as the copper sleeve 3 is of similar internal cross-sectional configuration and conforms closely to the iron or steel core member 2, I have chosen by way of iilustration a core member 2 of substantially circular cross section and a'tubula copper sleeve 3. A circular cross section is preferable because it allows the least mean length of copper circuit around the iron, thereby to minimize the resistance and weight of the copper.

In forming the core of my relay to provide s. structure in which substantially the entire frame is encased in copper and of unitary structure to avoid joints and undesired air gaps, I place a straight copper sleeve over a straight bar of solid or unlaminated magnetizable iron or steel and bend the bar and sleeve together to bring the ends of the tar close together. The copper sleeve is of such internal diameter that it fits closely over the core membe 2 and has Just sumcient clearance to -allow easy manual positioning of the sleeve upon fcore member before bending, Where the slew. and bar are circular, as in the embodiment of the ,invention shown, the ratio of the diameter of the 4 slightly less than, the length of the magnetizable core member 2. It has been found that for maxi mum time delay in drop-out the optimum ,ratio of length of copper sleeve to length of magnetic circuit is 1.

After the straight sleeve has been slipped over the straight frame member the bar and sleeve together are inserted in a suitable die having stop members arranged to define theposition of the sleeve upon the bar, and the sleeve and ba are bent together into the shape of a U or other equivalent shape to bring the ends of the magnetizable bar into juxtaposition. In this way the length of the magnetic circuit between the ends of the magnetizable core is made short relative to the length of the entire magnetic circuit including the core. Since the copper sleeve encircles the magnetic core for substantially its entire length, it is evident that the ratio of length of sleeve to length of magnetic circuit ismade to approach 1.

In bending the magnetic core and copper sleeve together, the magnetizable bar 2 is slightly deformed at its bight region, so that its cross section at the bight, while circular before bending, takes on v a slightly elliptical configuration, as shown at Fig. 4. Such deformation causes the sides of the core to press outwardly against the copper sleeve in the bight region, thereby firmly to hold the sleeve in position upon the core. Furthermore, in bending the copper-encased core, the outer side of the copper sleeve is stretched tightly over the core and the inner side of the copper sleeve is compressed against the inner surface of the core at the bight. Thus, in the region of the bight, the sleeve and magnetizable core are tightly clamped together around substantially the entire cross-sectional periphery of the core. so that the sleeve is fixed against sliding.

movement on the core.

If it is assumed that the exciting windings I9 and 20 are disposed to establish fluxes in opposing directions, the relay armature I is picked up by energizing either one or the other of the coils I9 or 2.. When it is desired to drop out the armature, the energized coil may be deenergized or, alternatively, the flux may be bucked down by energizing the opposing neutralizing coil. In either case, the decay of flux in the magnetic circult of the relay is delayed by circulating currents established in the copper sleeve 3. The flux decays exponentially until it reaches a value insuilicient to maintain the relay armature! in its picked up position. As mentioned hereinbefore, the flux decay takes place very gradually because of the substantial total enclosure of the relay frame in the copper sleeve 3. Relays built in accordance with my invention have been found to exhibit considerably longer time delay in dropout than do conventional relays of similar size and weight.

While I have described only a preferred embodiment of my invention by way of illustration, many modifications will occur to those skilled in the art and I, therefore, wish to have it understood that I intend in the appended claims to cover all such modifications as fall within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent in the United States is:

1. An electromagnetic time element device comprising an integral magnetizable core curved to provide a pair of juxtaposed polar ends, a sleeve of substantially non-magnetic electric conducting mridl once-sing said core for substantially its full length, a movable armature providing a magnetic circuit between said polar ends, and an exciting winding encircling said core to establish a magnetic flux therein.

2. An electromagnetic time element device comprising an integral magnetizable core curved to provide a. pair of juxtaposed polar ends, a sleeve of substantially non-magnetic electric conducting material encasing said core for substantially its full length, a movable armature having opposite ends arranged for cooperation with said polar ends, and an exciting winding encircling said core to establish a magnetic flux through said core and armature.

3. An electromagnetic time element device comprising an integral core of solid magnetirable material formed to provide a pair of juxtaposed polar ends, a sleeve of substantially non-magnetic low resistance electric conducting material encasing said core for substantially its entire length, an armature member centrally pivoted for movement of its opposite ends toward and away from said polar ends respectively, means for biasing said armature member to a position spaced from said polar ends, and an exciting winding encircling said core to establish therein a magnetic flux for attracting said armature.

4. An electromagnetic time element device comprising a substantially U-shaped integral magnetizable coreof approximately circular cross section providing a pair of juxtaposed polar ends, a substantially non-magnetic annular sleeve of low resistance electric conducting material encasing said core for substantially its entire length, the ratio of the diameter of said core to the diameter of said sleeve being of the order of 0.6, a movable armature cooperating with said polar ends, and an exciting winding encircling said core and disposed to establish a magnetic flux therein.

5. An electromagnetic time element device comprising a substantially U-shaped "integral core member of solid magnetimble material having an approximately circular cross section, a substantially non-magnetic annular sleeve of low resistance electric conducting material encasing said core for substantially its entire length, the ratio of the diameter of said core member to the external diameter of said sleeve being of the order of 0.6, a pole piece extending from one end of said core member to provid with the other end of said member a pair of oppositely disposed pole faces, a rotatable armature positioned in attractive relation with respect to both said pole faces and biased to a position spaced fromsaid faces, and an exciting winding encircling said core member to establish therein a magnetic flux for attracting said armature.

ROBERT C. RING.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Sweden Sept. 10,1932 

